The invention relates generally to methods for sterilizing membranes comprising oxidoreductases, such as glucose oxidase and associated biosensors.
Biosensors comprising membranes comprising glucose oxidase are used for continuous and/or automatic monitoring of glucose in bodily fluids such as in the blood stream or in interstitial fluid of certain individuals such as those with diabetes. Biosensors comprising membranes comprising the oxidoreductases glucose oxidase, lactate oxidase and glutamate oxidase are also used to automatically and/or continually detect the level of glucose, lactate and glutamate respectively in bioreactors to monitor the cell growth.
It is important that the biosensors are sterile to prevent at least potential damages from biological contaminant or pathogen (bacteria, fungi and viruses etc.) to the health and safety of the user or to the normal operation of the bioreactor.
Gamma irradiation, autoclave treatment, and ethylene oxide treatment, are some of the techniques for sterilization. However, besides eliminating/inactivating the unwanted and potentially dangerous biological contaminant or pathogen, the gamma radiation also damages the membranes comprising e.g. glucose oxidase and decreases the sensitivity of the biosensors. Therefore, methods have been developed to protect the biosensor and/or the membrane comprising glucose oxidase while sterilizing the biosensor and/or the membrane comprising glucose oxidase.
For example, US Patent Application Publication No. 2010/0293892 discloses a method of packaging an enzyme (glucose oxidase) sensor that prevents damage to the enzyme sensor and that maintains the sterility of the enzyme sensor by inflating the package with excess pressure of an inert gas or drawing a vacuum on the package before sealing the package and exposing the sealed package to radiation.
Options have also been explored to sterilize other biological materials without substantially damaging the biological materials. For instance, it is disclosed in U.S. Pat. No. 7,848,487 that urokinase, immobilized anti-insulin monoclonal antibody, and porcine heart valve cusps, after gamma irradiation in a non-aqueous environment, are able to maintain their function, but, after gamma irradiation in an aqueous environment (phosphate buffer saline solution, PBS), they lose their function significantly. In addition, US Patent Application Publication No. 2002/0044884 discloses that after gamma irradiation in a container containing a PBS solution as a filling liquid, the activity of anti-human CD4 monoclonal antibody disappears without the presence of a trisaccharide or higher saccharide having a positive charge, but maintains its function in the presence of a trisaccharide or higher saccharide having a positive charge.
It is found that by using the currently available methods, such as those proposed in the patents/patent applications mentioned above, to sterilize the biosensor and/or the membrane comprising oxidoreductases by gamma irradiation, the loss of sensitivity of the biosensor is too high in certain application environments.
Therefore, there is a need to develop a new method for sterilizing the biosensor and/or the membrane comprising oxidoreductases.